The present invention relates to a surface-mount type antenna for use in a global positioning system, more particularly to a surface-mount type antenna mounted on a portable remote terminal, and to a mobile communication terminal using the same.
A system having a global positioning system mounted on a portable remote terminal for transmitting information of the present position of the terminal to a specific party on the other end of the connection is being put to practical use. For example, when a carrier of the portable remote terminal meets an emergency (such as a traffic accident), the person can transmit information of his or her present position to a specific place (such as a rescue center) so as to take a necessary measure without delay.
As antennas used on such a portable remote terminal, surface-mount type antennas have frequently been used because of the terminal being limited in size. For example, a surface-mount type antenna disclosed in Japanese Patent Non-examined Publication No. H7-221537 has a configuration of a radiator electrode provided by a through hole formed parallel to a principal face of a dielectric substrate and of a through hole formed in the direction of the thickness of the dielectric substrate for electrically connecting a radiator electrode with a feeder electrode. In an art disclosed in Japanese Patent Non-examined Publication No. H7-235825, a radiator electrode and a coplanar type feeder line are provided on each of the principal faces of a dielectric substrate and they are connected by a through hole.
In both of the antennas described above, since high precision is required of the size of the through hole and, further, the input impedance of the antenna is directly affected by a connection made at the through hole, great variations in characteristics were produced between products.
In the case of a surface-mount type antenna disclosed in Japanese Patent Non-examined Publication No. H9-214226, it is attempted to miniaturize the antenna by embedding the feeder electrode in the substrate. However, productivity was poor because such a process as to cement substrates together was required and, sometimes, great variations in characteristics were produced. In addition, because of difference of thermal expansion coefficient between the substrate and the feeder electrode, cracks were produced, or stress was accumulated, in the substrate, and, sometimes, variations in characteristics were produced.
Further, an antenna disclosed in Japanese Patent Non-examined Publication No. H11-112221 is designed to achieve miniaturization by such a layout that a feeder electrode is surrounded by a radiator electrode. In this case, a minute distance was preset between the feeder electrode and the radiator electrode early in the designing stage to provide the antenna with required impedance matching.
Accordingly, this type of antenna lacks adjustment means and hence variations in characteristics between products sometimes became considerably great, depending on the manner of fabrication.
Further, in a surface-mount type antenna disclosed in Japanese Patent Non-examined Publication No. H11-74721, it is arranged such that the radiator electrode and the ground electrode are provided on the same principal face, whereas no particular design is made to decrease occupied areas by the two electrodes. Accordingly, the dielectric substrate becomes large in size and, therefore, miniaturization of the antenna has been difficult to achieve.
There has been such a technical problem with these prior art surface-mount type antennas that miniaturization of the product, decreased variations in characteristics between products, and increased productivity and enhanced reliability on the product cannot be attained at the same time.
In view of the problem described above, it is an object of the present invention to provide a surface-mount type antenna being small in size, producing small variations in characteristics between products, and being excellent in productivity and reliability, and, in addition, to provide a communication terminal using the same.
A surface-mount type antenna to be mounted on a printed circuit board of the present invention comprises: a substrate; a radiator electrode provided on a first principal face of the substrate; a ground electrode provided on its second principal face; a first feeder electrode having at least a portion thereof provided on the second principal face and on a side face of the substrate; and a second feeder electrode provided on an inner wall face of a hole formed in the side face, or, more particularly, formed on the first feeder electrode and located between the radiator electrode and the ground electrode.
Further, the first feeder electrode and the ground electrode are kept in a non-contact state and the first feeder electrode and the second feeder electrode are in electrical contact.
Instead of providing the second feeder electrode within a hole, it is possible to use, as the second feeder electrode, a feeder electrode provided on a stepped face of a stepped portion formed by cutting step-wise a portion of the side face on the side of the second principal face and close to the first feeder electrode. In this case, it may also be practiced to provide additionally a second ground electrode on a stepped face of a stepped portion formed by cutting step-wise a portion on the side of the second principal face of each of four side faces of the substrate and have this electrode electrically connected with the ground electrode provided on the second principal face.
As another type of second feeder electrode, a feeder electrode provided on an inner wall face of a groove formed in the second principal face can be used and, thereby, ease of fabrication can be obtained. As a further type of second feeder electrode, such a feeder electrode can also be used that is provided on an inner wall of a groove formed at a portion of the side face, on which the first feeder electrode is provided, parallel to the first and second principal faces.
By virtue of the above described structure, the surface-mount type antennas according to the present invention and communication terminals using the antenna can achieve miniaturization, reduction of variations in characteristics between products, and increase in productivity of and reliability on the products.